Cross-compilation failure for Darwin targets: test discovery on Linux host

[johnathan79717]

Description

Both darwin-arm64 and darwin-amd64 preset builds fail during the CMake build process when GoogleTest attempts to run test discovery on Darwin/macOS executables from a Linux build host. The cross-compiled binaries cannot be executed on Linux, causing the build to fail.

Steps to Reproduce

1. Configure the darwin-arm64 preset:

   cd barretenberg/cpp
   cmake --preset darwin-arm64

2. Build the project:

   cmake --build build-darwin-arm64 -j$(nproc)

Similarly for darwin-amd64:

1. Configure the darwin-amd64 preset:

   cd barretenberg/cpp
   cmake --preset darwin-amd64

2. Build the project:

   cmake --build build-darwin-amd64 -j$(nproc)

Error Messages

darwin-arm64:

/mnt/user-data/jonathan/aztec-packages-2/barretenberg/cpp/build-darwin-arm64/bin/crypto_blake3s_full_tests: 4: Syntax error: ")" unexpected
CMake Error at /usr/share/cmake-3.28/Modules/GoogleTestAddTests.cmake:112 (message):
  Error running test executable.

darwin-amd64:

/mnt/user-data/jonathan/aztec-packages-2/barretenberg/cpp/build-darwin-amd64/bin/crypto_blake2s_tests: 1: ����h��!H__PAGEZEROx__TEXT__text__TEXT�,���,�__stubs__TEXT�: not found
/mnt/user-data/jonathan/aztec-packages-2/barretenberg/cpp/build-darwin-amd64/bin/crypto_blake2s_tests: 7: Syntax error: ")" unexpected
CMake Error at /usr/share/cmake-3.28/Modules/GoogleTestAddTests.cmake:112 (message):
  Error running test executable.

Root Cause

The build system is using GoogleTest's automatic test discovery feature (gtest_discover_tests) which attempts to execute the compiled test binaries to discover test cases. When cross-compiling for Darwin/macOS on a Linux host, these Mach-O executables cannot be run on Linux, resulting in syntax errors when the shell tries to interpret them as scripts.

The error messages show:

• Binary format signatures being interpreted as shell commands (e.g., __PAGEZERO, __TEXT)
• Shell syntax errors when encountering binary data

Suggested Fix

Several possible solutions:

1. Disable test discovery for cross-compilation: Use gtest_add_tests instead of gtest_discover_tests when cross-compiling
2. Conditional test discovery: Only enable automatic test discovery when not cross-compiling:

   if(CMAKE_CROSSCOMPILING)
     gtest_add_tests(TARGET ${test_target})
   else()
     gtest_discover_tests(${test_target})
   endif()

3. Use BUILD_TESTING flag: Allow users to disable test building entirely during cross-compilation:

   option(BUILD_TESTING "Build tests" ON)
   if(BUILD_TESTING AND NOT CMAKE_CROSSCOMPILING)
     # Add test targets
   endif()

4. Defer test discovery: Use DISCOVERY_MODE PRE_TEST to delay discovery until test execution time (when presumably on the target platform)

Environment

• Build presets: darwin-arm64, darwin-amd64
• Host system: Linux
• Target system: Darwin/macOS
• Toolchain: OSXCross with Apple SDK
• CMake version: 3.28
• Affected component: GoogleTest test discovery

Impact

This prevents cross-compilation of the project for macOS/Darwin targets from Linux hosts, which is critical for:

• CI/CD pipelines that build for multiple platforms
• Linux-based build servers producing macOS binaries
• Developer workflows on Linux targeting macOS

Workaround

As a temporary workaround, users can:

1. Build without tests by modifying CMakeLists.txt to skip test targets
2. Build on native macOS hardware instead of cross-compiling
3. Use a macOS VM or container for building

[johnathan79717]

Not sure whether we'll run into this when we tried to publish .a files for our rust crate. Leaving it here for now.

[johnathan79717]

I don't think we need this. We're cross compiling with zig presets now.